The present invention generally relates to a combustion apparatus for burning fuel at a high excess air ratio and more particularly, to a burner for reducing the production of nitrogen oxides (hereinbelow, referred to as "NOx") in exhaust gas and enlarging the stable flame region, which is used for high-load combustion.
Problems of air pollution due to exhaust gas produced by combustion have been studied. As effective countermeasures against the problems, multistage combustion, gas mixing combustion, dividual combustion, etc. have been employed but NOx under about 50 ppm in exhaust gas cannot be achieved by these known combustion methods. A burner for domestic use has been proposed in which NOx of 10 ppm or so in exhaust gas can be achieved by employing premixed combustion. However, the prior art burner based on premixed combustion has disadvantages relating to its practical use because of its small variable ranges with respect to combustion achieved and air capacity because the stable flame region therein is narrow and that because if the excess air ratio is increased and reduced for changing the air quantity during the adjustment of the caloric, the flame is readily blown off and backfire takes place, respectively.
Meanwhile, in the combustion methods other than the premixed combustion method, it is extremely difficult to restrict NOx in exhaust gas to 10 ppm or so at the present time. Therefore, in order to restrict NOx in exhaust gas to 10 ppm or so, it is necesaary to enlarge the stable flame region in premixed combustion.